Aim: To investigate the alterations of placental P-glycoprotein (P-gp) and cytochrome P450 1A1 (CYP1A1) at different gestational days (GD), and to explore the possible significance of placental P-gp and CYP1A1 in tobacco smoke-induced intrauterine growth retardation (IUGR) in rats. Methods: An IUGR model was produced by passive tobacco smoking from GD 7 to parturition (GD 21) and predicted using fetal development parameters. Placental structure and function were monitored by observing pathological alteration and antioxidative function, including the content of malondialdehyde and the activities of superoxide dismutase and catalase (CAT). The expressions of CYP1A1 and P-gp (mdr 1a and mdr 1b)were detected using a reverse transcription polymerase chain reaction and immunohistochemistry. Results: Placental pathological changes occurred and the malondialdehyde content increased, whereas the activities ofsuperoxide dismutase and CAT lowered, when compared to their controls. In the rat placenta of the tobacco group, the level of CYP1A1 mRNA increased significantly; the level of mdr1a mRNA increased significantly at GD 21 but not at GD 14, whereas the level of mdr1b mRNA in different term remained stable; the expression of P-gp increased significantly only in full-term placenta. Conclusion: The expression of placental CYP1A1 and P-gp increased in tobacco-induced IUGR. Overexpression of placental CYP1A1 can attribute to the metabolism of tobacco and the generation of reactive metabolites, which can trigger IUGR. As a compulsory mechanism,upregulation of P-gp might decrease tobacco exposure to a developing fetus with IUGR.